The present invention relates to a distribution-type fuel injection pump for supplying fuel to a diesel engine or the like.
A distribution-type fuel injection pump is known from, for example, Japanese Patent Provisional Publication Nos. SHO 62-243962, SHO 62-258125 and SHO 62-258157. The known injection pump comprises a housing which is composed of a hollow body whose one end opens, and a head closing the opening of the body. The body and the head cooperate with each other to define an internal space within the housing. A feed pump is arranged at an end of the internal space on the opposite side from the head. The internal space has a major portion thereof which serves as a fuel chamber in which fuel discharged from the feed pump is stored.
A barrel is supported by the head. A drive shaft extends through a portion of the body on the opposite side from the barrel and is supported by the portion of the body in coaxial relation to the barrel. Rotation of an engine is transmitted to the drive shaft to rotate the same. The drive shaft has an inward end which is exposed to the fuel chamber. A plunger has one end thereof which is connected to the inward end of the drive shaft in coaxial relation thereto. Thus, rotational motion of the drive shaft is transmitted to the plunger.
The fuel chamber within the housing serves also as a cam chamber in which a cam mechanism is accomodated. The cam mechanism comprises a roller holder, a plurality of rollers rotatably supported by the roller holder, a cam disc connected to the one end of the plunger in contact with the rollers, and at least one spring biasing the plunger and the cam disc toward the rollers. The cam mechanism gives axial reciprocative movement to the plunger when the same rotates.
The plunger has the other end which is inserted in the barrel for axial reciprocative movement therealong. The barrel and the plunger cooperate with each other to define a fuel pressurizing chamber. The housing is formed therein with a fuel supply passageway, and a plurality of fuel discharge passageways corresponding in number to cylinders of the engine. The fuel supply passageway cooperates with a plurality of passages formed in the plunger to supply fuel within the fuel chamber to the fuel pressurizing chamber at a backward or return stroke of the plunger. The fuel discharge passageways cooperate with another passage formed in the plunger to supply the pressurized fuel within the fuel pressurizing chamber successively to the cylinders of the engine at a forward stroke of the plunger.
The fuel filled in the fuel chamber serves as lubricating oil for the cam mechanism. Accordingly, there is provided a sufficient lubricating effect with respect to the cam mechanism, if light oil that is regular fuel for the diesel engine is used as the fuel. However, if a user, who does not know that the fuel serves also as lubricating oil, employs fuel lighter in quality than the light oil such as, for example, kerosene or lamp oil in substitution for the light oil, lubrication with respect to the cam mechanism becomes insufficient. Thus, a surface layer is separated from each roller and the cam disc which are in contact with each other under the strong resilient or elastic force of the spring. The separated surface layers impede motion of the component parts within the housing.
Japanese Patent Provisional Publication No. SHO 60-147544, Japanese Utility Model Provisional Publication No. SHO 61-140171 (corres. to United States Ser. No. 06/824,963) and Japanese Utility Model Provisional Publication No. SHO 61-114069 (corres. to U.S. Pat. No. 4,697,565) disclose an arrangement in which a major portion of the internal space is used only as a cam chamber, and lubricating oil is received in the cam chamber. A fuel supply passageway bypasses the cam chamber, and the feed pump communicates with the fuel pressurizing chamber through the fuel supply passageway. With such arrangement, the cam mechanism can be well lubricated by the lubricating oil regardless of the type of the fuel. However, the arrangement is disadvantageous in that, since the fuel supply passageway utilizes a pipe connected to the housing, the pump is complicated in construction.
Additionally, Japanese Utility Model Provisional Publication No. SHO 62-88876 (corres. to U.S. Pat. No. 4,763,611) and Japanese Utility Model Provisional Publication No. SHO 62-165465 disclose a technique relevant to the invention. In pumps disclosed in these publications, however, a major portion of the internal space within the housing is utilized as a fuel chamber, and a cam mechanism is arranged within the fuel chamber.
On the other hand, the previously mentioned pump has the following additional problem. Specifically, component parts of the cam mechanism are accommodated into the body through the opening thereof. At this time, the spring is accommodated in the body under such a condition that the spring has its natural length. Subsequently, the spring is compressed by the head when the head is fixedly mounted to the body. Since high precision is required for operation of assembling various component parts into the pump, the operation normally relies upon human hands or power. For this reason, there is a limit in the force for retaining and holding the spring so that it is difficult to sufficiently strengthen the elastic force of the spring. Thus, jumping of the plunger cannot sufficiently be restrained during running. Further, in order to fixedly mount the head to the body, it is required that bolts extending through the head are screwed into the body while urging the head against the body against the biasing force of the spring. Thus, working or operating efficiency is low. Furthermore, when the spring is accommodated into the body, it is required that the position and posture of the spring are corrected through an opening formed in the peripheral wall of the body. Also in this respect, the working or operating efficiency is low.